Petrography and geochemistry of Oligocene bituminous coal from the Jiu Valley, Petroşani basin (southern Carpathian Mountains), Romania

Belt samples of Oligocene (Chattian) bituminous coal from 10 underground mines located in the Jiu Valley, Hunedoara County, Petroşani basin, Romania, have been examined and analyzed for proximate and ultimate analysis, major-, minor- and trace-element chemistry, organic petrography, and vitrinite reflectance. The mineral chemistry and mode of occurrence of trace elements also have been investigated using SEM and electron microprobe techniques. Twenty coal beds occur in the Jiu Valley and most of the samples are from bed no. 3, the most productive bed of the Dîlja-Uricani Formation of Oligocene age. The Petroşani basin, oriented SW-NE, is 48-km long, 10-km wide at the eastern part and 2-km wide at the western part. The coal mines are distributed along the center of the valley generally following the Jiu de Vest River. Reflectance measurements indicate that the rank of the coals ranges from high-volatile B to high-volatile A bituminous. Overall, rank decreases from the southwest to the northeast. In bed no. 3, Rmax varies from 0.75% in the northeast to 0.93% in the southwest. Although, most Oligocene coals in Romania and adjacent countries are lignite in rank, the Jiu Valley bituminous coals have been affected by regional metamorphism and attending hydrothermal fluids related to the Alpine orogenic event. The coals are all dominated by vitrinite; resinite and funginite are important minor macerals in most of the coals. Pyrite and carbonate generally dominate the mineral assemblages with carbonate more abundant in the northwest. Siderite occurs as nodules and masses within the macerals (generally vitrinite). Dolomite and calcite occur as fracture fillings, plant-cell fillings, and in other authigenic forms. Late-stage fracture fillings are siderite, dolomite, calcite, and ankerite. In one instance, two populations of siderite (∼ 35 and ∼ 45 wt.% FeO) plus ankerite fill a large fracture. Late-stage pyrite framboid alteration is Ni- and Cu-bearing, with Ni-rich pyrite, hydrated Ni, Fe sulfate, chalcopyrite and rare pentlandite and clausthalite. Some of the mines sampled in 2001 have been closed as Romania has undergone severe economic and environmental reforms in preparation for its 2007 entry into the European Union (EU). Romania's continued efforts to adapt to a market economy within the environmental and economic constraints of the EU make this collection of data valuable as the eventual fate of the other mines in Jiu Valley is unknown.